Compressor Bearings Research Articles

Enhancing stability and rheological behavior of nanolubricants for hermetic compressor bearings

The use of nanoparticles as nanoadditives in lubricating oils for hermetic compressor bearings presents a potential alternative to conventional additives. Alumina nanoparticles stand out as a promising candidate because they significantly improve lubrication by filling surface asperities, reducing friction and wear. Additionally, their large-scale production and lower cost, coupled with their environmentally friendly nature, make them an attractive option. However, the rheological behavior and stability of the lubricants must be evaluated, as nanoparticles can agglomerate and sediment. In this work, nanolubricants containing 0.5 and 1 vol% of pure alumina (A) and surface-modified alumina (AS) were prepared using a two-step method. Visual inspection and accelerated stability tests were conducted to evaluate the stability of the nanofluids. Rheological behavior was examined at temperatures of 25, 50, and 75 °C across shear rates up to 70,000 s−1, pertinent to hermetic compressor bearing applications. The results demonstrated that AS nanolubricants remained stable for an additional 1–2 weeks compared to A nanolubricants, which can be attributed to the chemical affinities of oleic acid with the oil. At 25 and 50 °C, both pure oil and AS nanolubricants exhibited Newtonian behavior, while A nanolubricants displayed slight pseudoplasticity, as confirmed by the Power Law model. At 75 °C, all lubricants exhibited thixotropic behavior.

Tilting Pad Journal Bearing Computational Fluid Dynamic Parametric Modeling for New Energy Transition Challenges

Abstract The necessity of increasing the efficiency and reducing the carbon foot-print of machines is pushing centrifugal compressor bearings design to higher and higher peripheral speed and lower oil consumptions especially in the new energy transition fields, resulting in an increase in the bearing temperatures. Therefore, the bearing thermal management starts to play a major role in extending the machine operability and reducing the maintenance frequency. A full three-dimensional (3D) parametric conjugate heat transfer computational fluid dynamic (CFD) model for tilting pad journal bearings (TPJBs) is introduced in this paper to address the temperature aspects of oil-film bearings. The parametric geometry of the model and the automatic mesh update, allow the equilibrium position search to be obtained without adopting any dynamic mesh algorithms. The tilting pad and rotating shaft equilibrium position are automatically calculated with a Newton–Raphson algorithm. The static performance of the TPJB is investigated for different journal diameters, bearing clearance, and operating conditions. The numerical results obtained are compared with experimental data from compressor mechanical running tests to demonstrate the reliability of the model presented. The 3D distributions of the oil pressure, velocity, and temperature given by the CFD model, can be locally optimized to face the new energy transition challenges.

High-Dimensional Mapping Entropy Method and Its Application in the Fault Diagnosis of Reciprocating Compressors

The effectiveness of feature extraction is a critical aspect of fault diagnosis for petrochemical machinery and equipment. Traditional entropy analysis methods are prone to disruption by noise, parameter sensitivity, and sudden entropy variations. This study establishes a high-dimensional mapping entropy (HDME) method characterized by robust noise resistance, addressing the issues of parameter sensitivity and inadequate noise suppression inherent in traditional feature extraction methodologies. A mapping theory of high-dimensional space based on kernel function pattern recognition is proposed, which reassembles the sample vector after phase space reconstruction of time series. The multi-scale high-dimensional mapping entropy (MHDME) and refined composite multi-scale high-dimensional mapping entropy (RCMHDME) algorithms are further studied based on the idea of refined composite multi-scale. Application to simulated signals shows that the suggested methods reduce parameter sensitivity and enhance entropy smoothness. The development of a methodology to identify faults through MHDME is proposed. This approach integrates signal preprocessing and intelligent preference techniques to achieve pattern recognition of reciprocating compressor bearings in various wear conditions. Moreover, the identification findings demonstrate that the suggested approach can effectively extract the characteristics of the signal and accurately distinguish the effects caused by different faults.

Analisis Kebutuhan Pelumasan saat Kegagalan Sistem Kelistrikan (Black Out) pada Kompresor Boil Off Gas (K-6801) pada Fasilitas LNG Hub

The lube oil system in the compressor plays an important role for any rotating equipment because it functions to provide lubrication against the effects of friction on various rotating equipment. This overhead tank works by gravity to distribute lubricating oil from operating speed to zero rpm. The large volume of lube oil provides lubrication to the compressor bearings when the normal circulating flow from the pump stops and is assisted by the backup flow from the overhead tank. The purpose of this approach is to calculate the need for lubrication when an electrical fault occurs in the Boil-off Gas compressor (K-6801). Based on the results of analysis and calculations where the Boil-Off Gas Compressor (K-6801) is the object of observation, the amount of lubricating oil needed for the remaining rounds is 1885 liters while the amount of lubricating oil available in the field is 1528,286 liters. From the calculation results, 1528,286 liters is sufficient based on the reference API Standard 614 edition 4, chapter 2, Section 1.4.10.2 because it has exceeded the 20% reduction from 1885 liters, namely 1508 liters. The height of the overhead tank that is suitable for flowing lubricating oil to the compressor bearings is 5.2588 meters above the compressor with a distribution pipe diameter of 3 inches and an orifice bore diameter of 1 inches.

Study on nitrogen barrier protection of an airend oil-free compressor bearings in H2 compression

The oil free compressors were specially designed for air compression. The National Research and Development Institute for Gas Turbines COMOTI gained a great deal of experience in producing/designing certified oil injection screw compressors for the natural gas field and for several years it has been focusing its research on the use of “dry” (oil-free) compressors in natural gas compression and more recently in hydrogen compression. Working with an explosive gas, one of an idea was to use a nitrogen barrier in oil bearing sealing, which are open source of gases in the atmosphere for such compressors. Worldwide, on-site nitrogen generators have been developed for a purity range of 95…99.5%, and that nitrogen can be supplied in any environment conditions. The present paper will address nitrogen flow with low percentage of oxygen for bearing sealing at the working pressure, the nitrogen consumption, ideas for H2 re-injection and the influence over the global efficiency of the process. Due to the Energy Strategy worldwide, and the studies regarding production, transport and storage of hydrogen in natural gas network, COMOTI has involved researches in developing such possibilities and to express a point of view in existing research in the newly created industry.

Fault diagnosis in reciprocating compressor bearings: an approach using LAMDA applied on current signals

Condition monitoring is one of the most important activities to implement predictive maintenance in industrial processes and perform fault diagnosis. Vibration is the most used signal for this purpose, however current signals arise as a non-intrusive alternative to condition monitoring. On the other hand, data driven approaches becomes as a way to develop fault classifiers by using Machine Learning. This paper proposes the development of a fault classifier for diagnosing failures in the bearings of a reciprocating compressor by using the current signals measured from the induction machine that power the mechanical device. The proposal applies cluster validity assessment for feature selection, and a LAMDA-based model for classification. Results show that this proposal can diagnose three failure modes with a precision over 90%.

Mixed elastohydrodynamic analysis of a coupled journal-thrust bearing system in a rotary compressor under high ambient pressure

The hermetic rotary compressor's bearings, including the thrust bearing, the main and sub bearings, work together under high ambient pressure. The thrust bearing works under light axial loads, but sever wear is found, which may be related to the crankshaft's misalignment and deformation and the high ambient pressure. To investigate this phenomenon, a complete coupled journal-thrust bearing model is constructed. The bearing forces are calculated with the mixed elastohydrodynamic model under high boundary pressure. The effects of the deformations and ambient pressure on the bearing performance are investigated. Results show that ignoring the crankshaft deformation makes the simulation underestimate the thrust bearing wear, and the high ambient pressure is the leading cause of the thrust bearing wear.

The effect of dynamics of the swash plate–slippers–piston assembly on friction torques in bearings in compressor of cooling aggregate

Abstract The swash plate type compressor utilized in car air conditioning devices and cooling system was analyzed in this study. Proper dynamic behavior of the components in such a compressor affected the correct functioning of the whole system. The aim of the study was to identify the characteristics of the main motion components in the swash plate–slippers–piston assembly of the compressor and to estimate the friction torques in its bearings. Some models of this assembly are elaborated and presented in the paper. The main components of slipper complex motion were identified, such as reciprocal motion along the axis of piston, rotation around piston axis, and short-time rotation around its own axis. Friction torque in axial bearing was higher than in journal bearing and varied with the rotational angle. Friction torques in journal bearings varied with the rotational angle and had different courses for two bearings of the compressor.

Determining Changes in the Engagement of Screw Rotors Due to Transmission Error

As a rule, the structural analysis of screw compressors during their design comes down to determining the geometric dimensions of the screws, the position of their window edges, as well as the gas forces acting on the compressor rotors. The latter determine the loads on the compressor bearings and affect vibration of the rotors and the compressor as a whole. Their effect plays the dominant role but not the only one. To create a mathematical model describing the vibration state of rotors, determining all additional forces acting on the compressor rotors that arise in the course of its operation under normal operating conditions is also required. These include the manufacturing inaccuracies causing skewing and bending of the rotor axles, as well as contact forces caused by the interaction of rotors due to their deviation from the nominal position. The latter are the least studied and, as a rule, are typical only for oil-flooded screw compressors with no rotor synchronisation mechanism. This article is devoted to the determination of rotor dynamics and the forces caused by rotor teeth engagement. In future, its results will serve as a basis for developing a rotor vibration state model. Meanwhile, the analysis of results obtained already at the current research stage allows to decrease their impact and effect.

Failure analysis of radial bearings used in the refining of petroleum products

The problem of premature failure of bearings is a common type of failure. In most cases, the destruction occurs due to violation of operating conditions. Since the destruction of bearings is a frequent occurrence, consideration of this special case of destruction in the future will help to avoid such problems. The object of research is the screw compressor bearings destroyed during operation. To identify the causes, a collapsed bearing was examined and a bearing that did not collapse during operation.

Determining the Coefficient of Efficiency for the Drives of Centrifugal and Piston Compressors

A formula of the coefficient of efficiency for the drives of centrifugal and piston compressors was derived. It takes into consideration the adiabatic work of gas compression, friction losses in compressor bearings and gas pressure losses in the compressor. In the past, gas pressure losses in the compressor were not taken into account and these arise due to the friction of compressed gas flows, and due to the fact that the gas needs to overcome local resistances and the bends in compressor cavities. The computation formula of the coefficient of efficiency of the compressor was converted and it is used for a separate computation of the two coefficients of efficiency of the drive, in particular the coefficient of efficiency that takes into account the adiabatic work of gas compression and the friction losses in the bearings and the coefficient of efficiency that takes into account only gas pressure losses in the compressor. The plots for the coefficient of efficiency of the drive that takes into consideration only gas pressure losses in the compressor were constructed for centrifugal and piston compressors. Practical computations of the coefficient of efficiency of the drive that depends only on gas pressure losses in the compressor were done for centrifugal and piston compressors. For the centrifugal compressor this coefficient of efficiency can reach the value of 0.01 and for the piston compressor this value can be equal to 0.02. The values of the second order should be taken into account when calculating and estimating the coefficient of efficiency of the drive of centrifugal and piston compressors.

Seeded Fault Testing and Classification of Dynamically Loaded Floating Ring Compressor Bearings

This paper investigates a variety of signal-monitoring and data-driven processing techniques to classify seed faults imposed on floating ring main crankshaft compressor bearings. Simulated main bearing shaft motion using an adaptation of the mobility method is first applied to demonstrate the plausibility of the method. Condition monitoring for three different fault types is experimentally investigated through seeded fault testing. A novel method for feature extraction utilizes a fast Fourier frequency-domain transformation coupled with a binning method that uses information across the entire frequency range. A principal component transformation process is then applied to reduce the dimension of the frequency-based feature vector to a small set of generalized features. A Bayesian classifier on the generalized features designed through seeded fault training data is shown to have excellent classifier performance across all fault types. A single-axis position measurement of the crankshaft shows the most promising results compared to a traditional accelerometer on the bearing housing and a novel accelerometer on the crankshaft. The single-axis measurement provides a cost-efficient alternative method to the two-axis orbit measurement typically used for traditional journal bearings.

Compressor Lubrication -the key to Performance

Today, Low Global Warming Potential Refrigerants are being evaluated, optimized and applied. Higher-pressure refrigerants, refrigerant blends, and new chemical families of refrigerants are candidates. Compressor designs and system components are being evaluated to deliver the desired capacity, efficiency and reliable performance for intended applications.Once the Refrigerant family is chosen based on Environmental and Heat transfer properties, System Chemistry between the Refrigerant and Lubricant families are scrutinized for optimum miscibility and solubility. These directly affect the Phase separation between the 2 liquid phases and reduction of viscosity. Over the entire Operating Envelope, the “oil return” and “viscosity reduction” problems are assessed. Compatibility aspects between chemicals (Refrigerants, Lubricants) and materials of construction (metallic, polymeric, elastomeric) are verified to avoid failures in use. System Components, compressor bearings, expansion devices and heat transfer coils are adversely affected due to contaminants circulating in systems. Rust, Copper plating, Formicary corrosion, elastomer swelling are example. Advances in Analytical Chemistry Techniques help the compressor and system manufacturers characterize the problems. Further, System Chemistry guides selection of lubricant additives.This presentation explains how lubricant selection is accomplished using Tribology and System Chemistry aspects.

Failure analysis of copper tube used in a refrigerating plant

This paper reports the failure analysis of a leaked copper tube used in a refrigerating plant for carrying polyol ester oil for lubrication and cooling of compressor bearings. Failure had occurred at the bent region of the tube in the form of a wide diametric crack. The crack was intergranular and filled with corrosion products. The failed region on the inner diameter side of the tube had red–brown and dull-black surface films which were identified as cuprous oxide. No degradation or decomposition of the lubricant oil was detected. The microscopic examination of the cross-section of the tube showed corrosion degradation on both the outer and inner diameter surfaces with similar morphology. The corrosion morphology consisted of pit tunnels with fine longitudinal cracks bridging individual pitted regions typical of ant-nest corrosion. A few cracks, at the bent region of the tube, had originated through the pits and propagated along the wall thickness. The failure was concluded to be due to ant-nest corrosion of copper in the presence of carboxylic acid. Organic compounds used during the fabrication and joining of the copper tubes, if not properly cleaned, may decompose to carboxylic acid in presence of air and moisture.

Effect of R600a on tribological behavior of sintered steel under starved lubrication

This paper describes the impact of the isobutane refrigerant on the wear performance of tribopairs at hermetic compressor bearings. The tribological behavior of 100Cr6 steel pin is investigated under starved lubrication condition in air and R600a environments when running against sintered steel which was treated with and without steam. EDS and SEM are carried out on pin and plate samples after wear tests. The results indicate that wear durability is lower for the tests with R600a than those with air. The adverse effect of R600a on wear rate is linked to the change in the viscosity and foaming characteristics of the oil in the presence of R600a as well as the lack of oxides.

Analysis of wear-fatigue damage and modification of compressor bearings

Wear-fatigue damage of two-layer (babbitt, bronze) bushings of piston compressor bearings are analyzed. The factors generating fretting wear and fatigue cracking are analyzed. The stress-strain state of a multimodule bushing of the standard and new designs (with auxiliary strengthening by a steel layer) has been calculated with the intent of modifying the friction joints. The proposed modification was found to ensure a twofold reduction of tensile stresses in the babbitt and bronze layers, decreased slippage, and pliability to fretting on the bushing backside. The modified bearings have shown a several-fold increase in their service life in the experimental industrial conditions.